Using a mapping node to disable tiling is streaching texture?
As mentioned by Róbert László Páli, this is an artifact of the way the mapping node works.

You can get around this using hjaarnio's technique:

Using this node setup that creates a map of where the image is:



Values in the 0-1 range are where the original image is, so if we use that as a mix factor:



It will use the Image texture only where the original image is mapped, and Base Color everywhere else. 

Base Color can be a texture or even another shader as well: